How do you implement a SIEM without drowning in alerts?

Implement a SIEM by deciding what questions it must answer before connecting sources. Name owners, choose a small set of high value log sources, define retention and protection, write a few detections tied to real attack steps, then widen. Projects that connect everything first tend to produce volume, not insight.

What is a SIEM, in NIST's terms?

NIST SP 800-92, the guide to computer security log management, defines SIEM software as a program that provides centralized logging capabilities for a variety of log types. SIEM products have one or more log servers that analyze logs and database servers that store them. The guide also notes that the broader term replaced older SEM products, focused on incident response, and SIM products, focused on auditing.

The guide describes two collection methods. Agentless collection means the server pulls logs from hosts or the hosts push to it, which avoids installing software but can send far more data over the network and may require the server to hold credentials for each host. Agent based collection installs a program on the host to filter, aggregate and normalize logs before sending. Pick per source, because sometimes only one method is feasible.

Why do SIEM projects stall?

Because "collect everything" is not a plan. SP 800-92 organizes the work into planning and operations. Planning covers defining roles and responsibilities, establishing logging policies, making sure the policies are feasible, and designing the infrastructure. Operations covers configuring log sources, analyzing data, responding to identified events, managing long term storage, and testing and validation.

Skipped planning shows up later as unowned alerts, missing fields, logs kept too briefly, and detections nobody trusts.

What should you connect first?

Choose sources by the attacks you want to see. Identity logs, since they show who signed in and what they changed. Endpoint and server operating system logs. Perimeter devices and remote access. Cloud control plane logs, which record who changed what. Key applications that handle sensitive data. CISA published a joint set of event logging best practices in 2024 with Australian and other international partners, which is a good second reference when deciding what to log and how to improve detection.

A rule of thumb is to add a source only when you can say which detection or investigation question it supports and who will look at the result.

How do you protect the logs themselves?

SP 800-92 treats log protection as its own challenge. A SIEM holds a record of everything that matters to an attacker covering their tracks, so it needs strict access control, integrity protection, time synchronization across sources, and a retention period that matches your obligations and investigation needs. Test that the retention actually holds: ask for a ninety day old event and see how long it takes.

A constructed example

A mid sized company connects 300 sources in the first month. The result is millions of events per day and 40 rules copied from a template. The on call analyst closes most alerts without reading them. After a reset, the team picks three scenarios: a login from a new country followed by a mailbox rule change, a new admin account created outside change windows, and an unusual volume leaving a database server. It connects the six sources those need, writes three detections with clear steps for the responder, and measures how long each alert takes to close. A month later it adds the next five sources.

How to check or apply this

1. Name an owner for the platform, owners for each log source, and an on call process for alerts.
2. Write the use cases first, as short scenarios with the log fields needed to detect them.
3. Choose log sources for those use cases and decide agent or agentless collection for each.
4. Normalize timestamps and key fields such as user, source address and host, and sync clocks.
5. Set retention per source, protect integrity and restrict who can edit or delete logs.
6. Write a runbook for each detection that says what to check and when to escalate.
7. Test with a simulated event and confirm it fires, routes to a person and is documented.
8. Review volume and alert quality monthly. Remove noisy rules or fix them. Then add sources.

Quick check

Sources

• NIST SP 800-92, Guide to Computer Security Log Management
• NIST SP 800-92, full text (PDF)
• CISA, Best Practices for Event Logging and Threat Detection

Last reviewed: 18 October 2026.